1. Field of the Invention
This invention relates to a magnetic tape cartridge and more particularly to a mechanism for preventing erasure of recorded video or audio signals.
2. Description of the Prior Art
For the prevention of unwanted or erroneous erasure of video or audio signals already recorded on magnetic tapes in cartridges, two different approaches have generally been considered; tab and plug types. The tab in most cases is formed in one piece with the cartridge housing and is adapted to be broken away to defeat further recording. It is used once for all, and for repetitive record-defeating some other means must be employed. The plug is usually not integral with the cartridge housing and has to be attached and removed for its function. Thus, the plug has the advantage of reusability but is inconvenient to handle; it must be fitted for each service with the necessity of subsequent removal and, moreover, the plug can sometimes be lost to view. Such a plug-type mechanism for preventing erasure of recorded video or audio signals, with which the present invention is concerned, depends on the plug position for opening or closing a detection opening to receive the detection feeler of the tape recorder (to prevent rerecording of video or audio signals) or keep off the feeder (for video or audio recording). With the cartridges of the prior art, however, the plug position is not readily observable from the outside; in order to make sure of the plug position inside it is necessary to peep through the detection opening.